if you are looking for second hand metric tyres, then you are either going to be searching for a long time, or have to fork out a lot of money for a new tyre/pair of tyres.
http://www.trademe.co.nz/motors/car-parts-accessories/wheels-tyres/alloy-wheels/auction-1285681130.htm
how about something like this? standard 15" basketweaves for about $200, has useable tyres to keep you going, and when the time comes to change them, they will be cheap as chips to replace since 15" tyres are plentiful.